Wafer transfer systems are used to provide an automated transfer of semiconductor wafers from one position to another position. For example, the wafers contained in a cassette may be moved individually to a processing chamber for depositing or patterning a layer of material. Alteratively, all of the wafers within a cassette may be transferred simultaneously for batch processing. Thus, it is necessary in some applications to remove all of the wafers from a cassette or other device in a single operation.
U.S. Pat. No. 4,449,885 to Hurtel et al describes a wafer transfer system for moving semiconductor wafers between a cassette and a processing chamber. The system includes a cassette conveyer assembly for properly positioning the cassette relative to an elevator blade which vertically raises and lowers individual wafers to and from the processing chamber. The elevator blade is actuated by a crank that is driven by a motor and a mechanical stepper. The crank is able to convert the rotary stepping motion of the drive motor to reciprocating linear motion having relatively low velocity near its end points and relatively high velocity near its midpoint. Thus, there is a high rate of wafer transfer with the area associated with a low risk of damage to the wafer.
Another linear wafer transfer system is described in U.S. Pat. No. 4,311,427 to Coad et al. The system provides automated handling and transfer of wafers individually and repetitively between processing stations and cassettes. A track-like conveyer engages a cassette having a number of wafers that are vertically aligned. The conveyer moves the cassette horizontally relative to a vertically movable blade that passes between the tracks of the conveyer and through the cassette to engage a single wafer. The wafer is then moved vertically to a processing chamber. In the operation of the processing chamber, the wafer is returned to the cassette or is deposited in a second cassette by the blade.
The transfer systems of Hurtel et al and Coad et al maintain the wafers in a vertical orientation during horizontal movement of the cassette and vertical movement of the elevator. This is at least partially a result of concerns regarding using automated equipment to shift semiconductor wafers between vertical and horizontal orientations. Semiconductor wafers are fragile devices that are susceptible to breakage. Moreover, minute particles will reduce the manufacturing yield of integrated circuit fabrication. Typically, contact with the wafers is limited to wafer edges, reducing the likelihood that surface scratches will occur. However, this renders it difficult to remove multiple wafers from a cassette and simultaneously change the orientation of the wafers.
What is needed is a device and system for batch handling fabrication articles, such as semiconductor wafers, such that the wafers can be tilted with little risk of damage.